1. Field of the Invention
The present invention relates to a system and method for calibration, set-up, and control of a selective wave solder system. More particularly, it relates to a system and method for accounting for positioning errors in the board and/or the system in during processing.
2. Discussion of Related Art
Many electronic devices use a circuit board as the foundation building block for the electronic circuitry which forms the device. With the advent of the printed circuit board (PCB), the board itself actually became part of the circuit, forming conductors for the electrical current between the various electronic components. The circuit board both supports the electronic components and links them together. Generally, the circuit board consists of a nonconductive base, such as fiberglass, coated with a thin layer of a conductor, such as copper, which is etched to form a pattern of electrical conductors. Components are then soldered to the circuit board. Soldering of the various components to a circuit board has generally been accomplished by using various techniques, such as: manual soldering, reflow soldering, batch soldering using a solder pot or continuous soldering using a wave soldering machine.
Wave soldering has long been the soldering method of choice for high production circuit boards which require through-hole parts. This is a continuous process in which circuit boards are passed over a wave of molten solder. The solder wets up through metal plated holes containing the component leads to consummate the soldering process. This process lends itself to automation, as the parts are simply loaded onto a conveyor which in turn passes the parts over a wide wave of solder. Advances in PCB technology, such as double-sided boards and mixed technology assemblies have allowed intricate and complex circuits to be implemented in a smaller footprint. However, these advances limit the feasibility of using historic wave soldering techniques.
The selective wave solder system was developed to achieve advantages of wave soldering on through-hole components in connection with complex circuit board assemblies. In one particular style of selective wave solder device, a circuit board is moved, using a gantry system, to different locations for processing. Flux and solder may be placed on discrete portions of the circuit board. Typically, the process points are selected through a teaching process. Using a manual control system, one moves the gantry with the circuit board through the system and identifies particular process points. The process points, identified as x, y and z values within the gantry system, are stored for automated processing. Furthermore, the file with the process points can be transferred and utilized on another selective wave solder machine for processing the same boards. In this manner, the processing of each board need only be entered once, independent of the number of production lines and selective wave soldering machines utilized in processing boards. During automated production, the gantry system will move to each of the stored process points and the pre-programmed action will be conducted.
However, often minor positional or rotational errors occur with the gantry system or placement of the circuit board. Circuit boards also have some variation in their fabrication which results in positional variations. Additionally, different machines may have variations in the placement of the modules or stations, which can results in positional errors. Variations within a machine may also occur upon servicing. These positional errors result in defects due misalignment of the process points and the work area on the circuit board. Therefore, a need exists for a system which can correct for variations in positioning of process points on a circuit board attached to the gantry system. A need also exists for a system which can correct for variations in the placements of processing devices.
Furthermore, circuit boards can sag or bow across the span of the board. This is particularly prevalent in large circuit boards with many components. The height of the solder wave may also vary over time due to variations in pump speed, solder levels, and environmental factors. The variations in board height, from sagging or bowing, and solder wave height can lead to defects. The relationship between the board height and the wave height determines the contact area, depth, and time of the solder operation. A board which is too high relative to the solder wave may result in incomplete solder joints. A board which is too low can become excessively hot, warp or destroy components. Therefore, a need exists for a system which can determine and correct for variations in board and solder wave height.